One time I clicked on a silly animated music video about how Mussolini screwed up invading Greece, and watching this whole 60 second clip flipped my entire youtube into alt-right mode. It was like night and day and it happened immediately.

I started getting suggested things like "Biggest Hillary Fails" and "Jordan Peterson DESTROYS WHOEVER" over and over and over, and it got quickly got darker with things about how problematic immigration was and weird fan "documentaries" about senior SS leaders.

I'm way too suspicious (to a fault) of everything I take in, but I can imagine other people going down real holes if they were served the same terrible suggestions.